| 摘要: | 氧化還原液流電池中，釩氧化還原液流電池（Vanadium Redox Battery, VRB），因具有在低成本與高效率的情況下存儲大量電能，近年來備受關注。VRB中的關鍵零件-多孔性碳電極，作為液體擴散層（Liquid Diffusion Layer, LDL），和質子交換膜燃料電池（Proton Exchange Membrane Fuel Cell, PEMFC）中的氣體擴散層（Gas Diffusion Layer, GDL）區別在於厚度，LDL厚度以毫米作為單位而GDL只有它的1/5 - 1/10。以厚的碳氈作為電極的其中一個原因是為了增強VRB內部的擴散長度，但應該要盡量降低多餘的電阻。而LDL的厚度還有著應力吸收體的作用，並保持離子交換膜與集電板的連接，確保膜電極組件(Memberane Electrode Assembly, MEA)的耐久性。而本研究的重點有兩個(1)多孔性碳氈在不同預壓量下(2)多孔性碳氈在無電解電鍍不同厚度的鎳後之電性、機械性質跟型態分析。(1) 多孔性碳電極在不同預壓量下之電性、機械性質跟型態分析
為了解LDL對電池性能的影響，本章節是對VRB中LDL（包括三個廣泛使用的多孔性碳電極和一個金屬泡棉）進行0-40％的壓縮並觀察其電性、機械性質和型態。由我們的實驗結果可以發現，電阻的大小是由夾持力與壓縮百分比所決定。而增加應力後，有很多現象是值得研究的，如MEAs的耐久度、電阻值的下降增加導電率、孔隙率的下降引影響質傳和多孔性碳電極對流道侵入。實驗結果發現，隨著夾持力增加，多孔性碳電極會因為肋而產生變形導致孔隙減少與侵入導致流道體積減小。
(2) 多孔性碳電極在無電解電鍍不同厚度的鎳後之電性、機械性質跟型態分析
本章節採用了新的無電解電鍍鎳之多孔性碳電極，討論其鍍層厚度對電性、機械性質與形態特性的影響。實驗結果發現，無電解電鍍鎳在多孔性碳電極上是可以有效的降低電阻，並在壓縮40%的後減少一半以上的片電阻(Areal Specific Resistance, ASR)，而應力 - 應變曲線、殘餘應變和孔隙率並沒有太大的差異。鍍鎳多孔性碳電極是一種很發展潛力的VRB電極材料。
Redox-flow batteries, in particular vanadium redox flow battery (VRB), are receiving intensive attention due to their ability to store large amounts of electrical energy in a relatively cheap and efficient scenario. One of the key components in VRB is carbon felt, which serves as the liquid diffusion layers (LDL) and differentiates distinctively from the gas diffusion layers (GDL) in proton exchange membrane fuel cell (PEMFC) such that the thickness LDL is in mm range, whereas GDL is only 1/5 – 1/10 of it. One reason for a significantly thick carbon felt is due to the enhancement of diffusion length for the VRB while the associated resistance should be minimized. While the thickness of LDL plays the role of stress absorber and maintains the conductivity and the electrical contacts, the durability of the MEA is reasonably safeguarded. The focus of the study are the electrical, mechanical and morphological properties of (1) carbon felt in different compression percentage (2) carbon felt after electroless plating (1) Electrical, mechanical and morphological properties of carbon felt in different compression percentage
Experiments including electrical, mechanical and morphological aspects under compression in the range of 0-40% have been carried out on four potential materials for liquid diffusion layer(LDL) of vanadium redox flow battery (VRB) (including three widely used carbon felt and one recently utilized metal foam) in order to better understand the influence of the fundamental properties on the battery performance. We experimentally demonstrate that the electrical contact resistance is predominately determined by the clamping force. It is observed that increasing the stress applied on the carbon felt, which is of high interest for the durability of the membrane electrode assembly (MEA), has moreover a positive effect on their performance due to the reduced contact resistance. However, a simultaneously reduced porosity is also recorded and possibly detrimental to the mass transport of vanadium electrolyte. Moreover, the intrusion of carbon felts under compression is also characterized. Experimental results show that with the clamping force increases, both the porosity of the carbon felts underneath the rib and channel volume decrease, and this can be mainly attributed to the deformation of the carbon felts and resultant changed of the void volume as well as intrusion.
(2) Electrical, mechanical and morphological properties of carbon felt after electroless plating
This research adopts a new Ni plating carbon felt and the effect of plating thickness on mechanical, electrical and morphological properties are also discussed. Experimental results show that the nickel coated carbon felt prepared by electroless plating was successfully applied and a drastically reduced ASR of 50% can be obtained under 40% compression, while the stress-strain curve, residual strain and porosity basically remain unchanged. The nickel coated carbon felt is a promising electrode material for VRB application. |
